Refining of lubricating oils



United States This invention has to do with the refining of petroleum lubricating oil stocks, and particularly those stocks containing parainic, naphthenic, olenic and aromatic hydrocarbons, with or without naphthenic acids, as obtained from topped crudes so constituted, for example the well known Smackover and California San Joaquin Valley type crudes.

These oils are composed of a complex mixture of different boiling point hydrocarbons having associated with them, various compounds which must be removed to produce a finished lubricating oil of good quality. Two general methods currently are employed for refining lubricating oil stocks. One method involves treatment of the oil with concentrated sulfuric acid, for example 98% sulfuric acid or even fuming sulfuric acid; the other method involving extraction of the oil with suitable solvents such as liquid sulfur dioxide, furfural and the like. Some refining procedures have combined both sulfuric acid treatment and solvent extraction. As is well known, using the solvent extraction type process permits substantial separation ot' aromatic hydrocarbons from the paraffinic and naphthenic hydrocarbons.

The action of concentrated sulfuric acid on lubricating oil stocks is extremely complex and commercially disadvantageous in various respects. The concentrated acid is a powerful oxidizing sulphating, sulphonating and polymerizing agent, and it is also known to have certain solvent characteristics. In general, its reactivity is influenced bythe acid concentration and the temperature and time of contact with the oil. ln comparison with the present invention, it is important to note that when lubricating oil stock is contacted with concentrated sulfuric acid, the acid reacts not only with unstable or unsaturated cornpounds which it is desired to remove, but the acid also reacts with and converts into sludge, compounds which may advantageously be left in the nished oil. Accordingly, it is desirable that refining of the lubricating oil stock be conducted in a manner which will remove a maximum of deleterious sludge forming compounds', while retaining in the oil a maximum of those desirable hydrocarbons which normally are lost through sulfuric acid treatment.

On the other hand, using solvents such as sulfur dioxide and furfural as rening agents, especially in the f treatment of lubricating oil stocks derived from Smackover, Arkansas and California San Joaquin Valley type crudes, there occur high losses (in the Lextract phase) of potentially valuable hydrocarbons through conversion into products of lower values than the hydrocarbons from which they are extracted. Such degradation of potentially valuable compounds may appear ultimately in asphaltic residues obtainable from the extract. Considering that the amount of such extracted material may be as high as say around 28% of the oil treated, it is apparent that much valuable oil is lost.

I have found that the presence of aromatic hydrocarbons, and particularly in controllable amounts, is highly desirable in a lubricating oil. The aromatic compounds have been found to act as proficient solvents, particularly in internal combustion engine lubricating oils, since at the operating temperatures these aromatic hydrocarbons dissolve the asphaltic binders which ordinarily tend to hold carbon particles together and form carbon deposits which may result in such undesirable effects as stuck piston rings, excessive carbon accumulations, and the like.

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frice It may be further observed that in an oil improperly constituted, the presence of aromatic hydrocarbons may be in excess of the most effective amount, everything considered, and that the excess may cause formation of crankcase sludges which produce such bad effects as rapid and excessive loading of oil filter elements. It becomes important, therefore, that the nature of the refining process be such as will permit in the oil an aromatic hydrocarbon concentration adequate to take full advantage of the desirable solvent properties of the aromatics, while avoiding sludge forming tendencies of excessive concentrations.

I have also found that a lubricating oil composed primarily of a mixture of paraffin and naphthene hydrocarbons should also contain a sufficient and controllable amount of such hydrocarbons as are extractable, for example with liquid sulfur dioxide, in order to accomplish two purposes; first, to best minimize friction between contacting moving parts, and second, to furnish the desirable solvent potential, particularly in oilsto be used for lubrication of internal combustion engines.

It is possible to over-refine a lubricating stock either by the excessive use of solvents or extreme concentrated sulfuric acid treatments, or both, with resultant production of an oil which is incapable of efficiently reducing friction which further tends toward rapid oxidation, and production of excessive amounts of lacquers, varnishes and corrosive acidic compounds. Thus, with respect to over-refined oils, or oils which may be decient for other reasons, it is important to make available those compounds which may be used to supplement the deficient oil to give to it the desirable lubrication and stable properties.

My general object is to provide an improved process for the refining most economically of such stocks to any of various degrees and to the production of various residual or byproducts, all in a manner avoiding the use of excessive sulfuric acid treating reagents, and to the elimination of the troublesome treating and sludge disposal problems characteristic of concentrated sulfuric acid treatments. In general, the invention contemplates a refining method whereby it is possible to remove from the crude lubricating oil stock, naphthenic acids and olens, and further if desired, to segregate parafnic and naphthenic components of the stock, all by a series of operations involving only straightforward and simple treating and distillation steps obviating, as indicated, the use of strong sulfuric acid reagents.

Particularly contemplated is the extraction, by polymerization and distillation, of olefinic or unsaturated hydrocarbons from the refining stock, and conditioning of the oil for further treatment to segregate its paraffinic and naphthenic components, by the use of a solution of aluminum sulfate as a polymerizing agent, in distinction to the customary sulfuric acid treatment used for extraction of unsaturated compounds subject to polymerization and conversion to sludge.

The invention may be understood most readily and to best advantage by proceeding directly to a detailed description of an illustrative procedure, the steps of which are indicated in flow sheet form by the accompanying drawing.

The lubricating oil stock to be refined may consist typically of a crude oil topped through its gas oil fraction and containing light, medium and heavy lubricating oil fractions, the constituency of which may or may not include naphthenic acids, together with olefnic or unsaturated hydrocarbons, as well as aromatic compounds. lf naphthenic acids are present, this unrefined stock may first be treated with sufficient alkali solution in an amount sufficient to neutralize the naphthenic acid content of the oil. The resulting mixture is then dehydrated by heating to a temperature sufficiently high to flash olf the water introduced by the alkali (e. g. a

soda) solution. The dehydrated mixture is then subjected to distillation under sub-atmospheric pressure that may be as low as 10 mm. of mercury absolute, to vaporize the lubricating oil fractions which together may constitute around 95 of the stock distilled. The neutralized naphthenic acid residue may be put to disposal or such by-product use as may be desired, e. g. recovery of soaps, naphthenic acids and production of asphalt.

The vapors from the vacuum distillation are condensed and the condensate is intimately mixed at a temperature below 212 F. with a solution consisting essentially of an aqueous solution of aluminum sulfate, the quantitative amount of aluminum sulfate used being suicient for the condensation or polymerization of the unsaturated or unstable compounds in the oil. Typically a 50% aluminum sulfate solution may be used, with the aluminum sulfate-to-oil ratio preferably under 10%. The resulting mixture first is dehydrated by heating to a temperature suicient to drive ofi the if um distillation stage are passed at a temperature rang- 0 ing between about 300 to 700 F., through a bed of adsorbent composed typically of fullers earth or any of various activated clays, on which may or may not be deposited a polymerizing agent such as aluminum sulfate, or any appropriate metal or metal salt. Desirably the vapors are prevented from undergoing appreciable condensation while passing through the adsorbent bed, as may be accomplished by insulating or independently heating the bed. The vapors are condensed to a product which may be used as a finished oil, or any particular fractions desired as finished oils, the chemical constituency of which is generally a combination of parainic, naphthenic and aromatic hydrocarbons. This oil is fully stabilized and may be used for various lubricating purposes.

However, for the production of lubricating oils and oil extracts to particular specifications, it is desirable that refining of the stock be continued to the extent of separating aromatics from the parafnic hydrocarbons. As illustrative, these may be present in the catalytically refined oil produced as described in the foregoing, Within the range of about 50 to 95% paraflins and naphthenes, and 15 to 40% aromatic hydrocarbons.

Preparatory to separation of the paraflnic and aromatic hydrocarbons by liquid sulfur dioxide treatment, for example, the condensate recovered following polymerizing treatment of the stock, is diluted with a relatively low boiling hydrocarbon, for example naphtha ordinarily in a proportion under 50% naphtha, to secure fluidity and good separation of the phases ultimately formed, and the resulting mixture is chilled to a suitable temperature, say around 14 F. (Using solvents such as furfural, dilution and chilling of the stock is unnecessary.) The diluted and chilled stock is intimately contacted with the liquid solvent at a temperature maintained at or below the boiling temperature of the solvent, for a period sufficient for dissolution of the aromatics in the liquid sulfur dioxide solvent, and sufficient for phase segregation of the dissolved and undissolved components of the oil. The phases are then separated into raffinate and extract stocks for further treatment.

The raffinate and extract are separately heated to drive off their sulfur dioxide content, which may be taken to an appropriate recovery system. By steam distillation of the sulfur dioxide-free raffinate, its naphtha content is vaporized and recovered, leaving an essentially parafinic and naphthenic oil residue which then may be vacuum distilled, with vor without fractionation, into different boiling range distillates. The vaporized fraction or fractions, constituting say 95 of the oil, are condensed as essentially parafiinic base treated lubricating oils.

Following removal of sulfur dioxide from the extract, the latter is steam distilled to vaporize off its naphtha content and produce a residual essentially aromatic stable oil which may be used as such, or fractionated to produce different boiling range aromatic distillates. This product, or these aromatic fractions, may be used independently as lubricating oils, or as additives to other oils or stocks, or all or any portion of the aromatic oil or fractions may be blended with the essentially paraffinic and naphthenic oil product obtained from the final vacuum distillation.

I claim:

l. The process of refining lubricating oil stock containing parafnic, naphthenic, olefinic and aromatic hydrocarbons, that includes mixing the liquid oil stock with liquid aqueous aluminum sulfate solution to disperse the aluminum sulfate in the oil, dehydrating the resulting mixture, then vaporizing the oil from the mixture under subatmospheric pressure and condensing the vapors, mixing the condensate with a lower boiling hydrocarbon and contacting the resulting mixture with a solvent to produce a raffinate phase which is predominantly paraffinic and naphthenic hydrocarbons and an extract phase which is predominantly aromatic hydrocarbons, distilling the rafiinate phase and recovering therefrom its lubricating oil content, distilling the extract phase and recovering therefrom its lubricating oil content, and adding a portion only of the aromatic hydrocarbons from the distilled extract phase to the distilled parafiinic and naphthenic phase to produce a final lubricating oil of lower aromatic hydrocarbon than the starting oil stock.

2. The process claimed in claim l, in which the oil stock contains naphthenic acids, and the stock initially is treated with an alkali to remove the naphthenic acids.

3. The process claimed in claim l, in which said solvent is of the group consisting of liquid sulfur dioxide and furfural.

4. The process of refining lubricating oil stock containing parafiinic, naphthenic, olefinic and aromatic hydrocarbons, that includes mixing the liquid oil stock with liquid aqueous aluminum sulfate solution to disperse the aluminum sulfate in the oil, dehydrating the resulting mixture, then vaporizing the oil from the mixture under subatmospheric pressure and condensing the vapors, mixing the condensate with a lower boiling hydrocarbon and contacting the resulting mixture with a solvent to produce a rainate phase which is predominantly parainic and naphthenic hydrocarbons and an extract phase which is predominantly aromatic hydrocarbons, steam distilling the raffinate phase to remove the solvent and then vacuum distilling the steam distilled ramnate and recovering therefrom its lubricating oil content, steam distilling the extract phase and recovering therefrom its lubricating oil content, and adding at least a portion of the aromatic hydrocarbons from the distilled extract phase to the distilled paraffinic and naphthenic phase to produce a final lubricating oil of lower aromatic hydrocarbon than the starting oil stock.

References Cited in the file of this patent UNITED STATES PATENTS 1,809,170 Lachman June 9, 1931 1,825,861 Gray Oct. 6, 1931 1,903,407 Pew Apr. 4, 1933 1,988,711 Bray et al. Jan. 25, 1935 2,035,610 Lachman Mar. 31, 1936 2,199,930 Walsko May 7, 1940 2,471,153 Hoover May 24, 1949 FOREIGN PATENTS 80,908 Germany Apr. 16, 1895 

1. THE PROCESS OF REFINING LUBRICATING OIL STOCK CONTAINING PARAFFIN NAPHTHENIC, OLEFIN AND AROMATIC HYDROCARBONS, THAT INCLUDES MIXING THE LIQUID OIL STOCK WITH LIQUID AQUEOUS ALUMINUM SULFATE SOLUTION TO DISPERSE THE ALUMINUM SULFATE IN THE OIL, DEHYDRATING THE RESULTING MIXTURE, THEN VAPORIZING THE OIL FROM THE MIXTURE UNDER SUBATMOSPHERIC PRESSURE AND CONDENSING THE VAPORS, MIXING THE CONDENSATE WITH A LOWER BOILING HYDROCARBON AND CONTACTING THE RESULTING MIXTURE WITH A SOLVENT PRODUCE A RAFFINATE PHASE WHICH IS PREDOMINANTLY PARAFFINIC AND NAPHTHENIC HYDROCARBONS AND AN EXTRACT PHASE WHICH IS PREDOMINANTLY AROMATIC HYDROCARBONS, DISTILLING THE RAFFINATE PHASE AND RECOVERING THEREFROM ITS LUBRICATING OIL CONTENT, DISTILLING THE EXTRACT PHASE AND RECOVERING THEREFROM ITS LUBRICATING OIL CONTENT, AND ADDING A PORTION ONLY OF THE AROMATIC HYDROCARBONS FROM THE DISTILLED EXTRACT PHASE TO THE DISTILLED PARAFFINIC AND NAPHTHENIC PHASE TO PRODUCE A FINAL LUBRICATING OIL OF LOWER AROMATIC HYDROCARBON THAN THE STARTING OIL STOCK. 